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> But that’s the thing, if our galaxy had lots of 20-21st century Earth level civilizations, we would be able to detect them with our existing SETI programmes.
by Chathamization 9y ago
> But that’s the thing, if our galaxy had lots of 20-21st century Earth level civilizations, we would be able to detect them with our existing SETI programmes.
But we couldn't. In general, SETI couldn't even detect such a civilization even if it was in the star system closest to earth:
> If an extraterrestrial civilization has a SETI project similar to our own, could they detect signals from Earth?
> In general, no. Most earthly transmissions are too weak to be found by equipment similar to ours at the distance of even the nearest star. But there are some important exceptions. High-powered radars and the Arecibo broadcast of 1974 (which lasted for only three minutes) could be detected at distances of tens to hundreds of light-years with a setup similar to our best SETI experiments.
The OP is right, in order for their to be a paradox we have to assume that civilizations much more advanced than ours are using a particular type of tech (the kind we're looking for, like radio broadcasts), that their using much stronger signals that we have ever used, and that the time period they used these hypothetical super powerful radio signals happens to be at the right time for us to encounter them. IE, let's say they used them for 2,000 years before moving on to other tech, but the signals only reached earth between 1,548,000-1,546,000 BC, or 450,000-458,000 BC, etc.
People are making a set of very, very specific assumptions based on little evidence. Then they see that the evidence that is available suggests that it's unlikely that every single one of their assumptions is correct, and they respond by calling it a paradox.
[1] https://www.seti.org/faq https://www.seti.org/faq
- davedx 9y agoOP said: 'the universe could full of earth-level societies and we wouldn't know'. It's a very extreme claim and the SETI FAQ answer directly contradicts it.
- mannykannot 9y agoThe SETI FAQ says that in the right circumstances, we might detect some of the closest ones, so the OP's statement is not contradicted.
- pavel_lishin 9y ago> But we couldn't. In general, SETI couldn't even detect such a civilization even if it was in the star system closest to earth. Your quote relies on us detecting re-runs of "I Love Lzcwwdrrr", but our telescopes can reliably do spectrographic analysis of faraway stars and planets these days. We'd likely be able to detect things like unnaturally high levels of hydrocarbons in otherwise oxygen-full atmospheres, and other industrial by-products. If Alpha Centauri had a planet with an industrial civilization, we might be able to spot city lights.
- gehwartzen 9y ago>Your quote relies on us detecting re-runs of "I Love Lzcwwdrrr", but our telescopes can reliably do spectrographic analysis of faraway stars and planets these days. We'd likely be able to detect things like unnaturally high levels of hydrocarbons in otherwise oxygen-full atmospheres, and other industrial by-products. We don't know what "unnatural" levels of CO2 on other planets are. > If Alpha Centauri had a planet with an industrial civilization, we might be able to spot city lights. We do not even remotely have that capability.
- joe_the_user 9y agoHmm, it is reasonable to speculate that once our sensor levels get much more accurate we might be able to sense fuzzy, indirect evidence of earth-level societies on other star systems though aggregates like city-light and pollutants. But that is a long way away from present day detection - we're detecting planets through planet going in front of them and other indirect approaches that don't yield detailed information. See: https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets https://en.wikipedia.org/wiki/Methods_of_detecting_exoplanet...